A sheet of logos allegedly used to stamp packets of heroin was found in a Bronx apartment. It was part of a seizure of $8 million worth of heroin.

NEW YORK — In a major drug bust that drew little attention just a week before Philip Seymour Hoffman’s death, authorities found a sophisticated heroin packaging and distribution operation in an apartment in the Bronx.

There, workers with coffee grinders, scoops and scales toiled around the clock to break down bricks of the drug into thousands of tiny, hit-size baggies bearing stamped brands such as “Government Shutdown” and, in a nod to the Super Bowl, “NFL.”

The seizure of $8 million worth of heroin was the result of the latest raid on heroin mills located behind the doors of New York homes, which authorities say are a sign of a well-oiled distribution network that caters to more mainstream, middle- and upper-class customers such as the Oscar-winning Hoffman.

Heroin dealers want to find customers with ready cash “who are going to be with them until they die,” said city Special Narcotics Prosecutor Bridget Brennan. “That’s the attitude.”

Tests are continuing to try to pinpoint how Hoffman died, but his body was found with a syringe in his arm and dozens of packets of heroin nearby. Where he got his drugs remains uncertain, but the arrests of drug suspects identified during the investigation suggest he might have visited a lower Manhattan apartment building where a supplier lived.

There’s no evidence that the Bronx operation provided any heroin Hoffman might have bought. But New York has long been known as the nation’s capital of smack, regularly accounting for about 20 percent of the heroin the federal Drug Enforcement Administration seizes every year.

Those seizures have grown by 67 percent in the state over the last five years, a trend Brennan attributes in part to high-volume heroin mills invisible to most New Yorkers but capable of churning out hundreds of thousands of packets within days after a shipment arrives.

The pipeline starts in Mexico, where cartels traffic Colombian-produced heroin by the kilogram. The wholesalers smuggle the drugs into the United States concealed in trucks, through tunnels dug under the Southwest border and, in one recent case, by molding and coloring the heroin to look like coffee beans and shipping it via UPS to a private postal box in Queens.

In the Northeast, the cartels have increasingly supplied Dominican middlemen who rely on a business model for heroin mills that emphasizes discipline, quality control and an absence of violence.

The retailers favor residential settings in safe neighborhoods as a means of cover. Raids by Brennan’s office and the DEA in recent years have found them in a newly renovated apartment in midtown Manhattan that rented for $3,800 a month and in a red-brick home in the New York City suburb of Fort Lee, N.J.

Workers can make up to $5,000 a week. They’re also given meals and toiletries to help make it through 12-hour shifts.

The mill operators and workers go out of their way not to disturb neighbors, who might report them to police, or to draw the attention of other criminals who want to rob them. They leave the apartments empty when not working and sometimes change locations long before their leases are up as a cost of doing business, said James J. Hunt, the acting head of the DEA’s New York office.

The economics are addictive: The heroin flooding the region carries an average wholesale price of about $60,000 per kilo. The retailers can cut a kilo to a 50 percent purity level using powdered vitamin B or other nontoxic substances. That provides enough drugs to fill 25,000 single-dose glassine envelopes that would be sold for $5 each to street-level dealers, who in turn charge customers $10 to $15.

After subtracting the cost of the kilo, wages and other expenses, the mill operator would turn a $70,000 profit per kilo.